(1) Field of the Invention
The present invention relates to the transfer of commands and storage data to a data storage device, for example over a databus, and is concerned with improving the rate of data transfers.
(2) Description of Related Art
Databuses are used to connect data storage devices with a host apparatus. Transfers of storage data, being the data of interest that is stored on the data storage device, occurs over the databus in either direction, that is from the host apparatus to the data storage device or vice versa. The transfers of storage data occur on the basis of commands that are transmitted from the host apparatus to the storage device. A wide range of types of databus are known. Typically, a standard specifies the nature of the databus, including the physical hardware of the databus and the data transfer protocol that specifies the format and timing of commands and storage data that are transferred. Examples of serial databuses include USB (Universal Serial Bus), SCSI (Small Computer System Interface), S-ATA (Serial Advanced Technology Attachment) and IEEE 1394. A controller is used to control the transfer of commands and storage data in accordance with the relevant standard.
An important performance parameter of a databus is the rate at which data is transferred. This will be dependent on the bandwidth of the databus and on the data transmission protocol. The transfer rate of individual bits of data is dependent on the bandwidth. The rate of transfer of storage data will be slower, additionally depending on the data transfer protocol which will impose an overhead on the transmission of storage data. It is desirable to maximise the rate of transfer of storage data and also the rate of transfer of commands. Standards are created with a view to this, whilst maintaining the reliability of data transfers.
Similar issues apply to transfers of data to a data storage device that is not over a databus.